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Precision vs accuracy

Published 24 March 2010

From
Steve Lonsdale

When David Shiga wrote that the Absolute Color Calibration Experiment for Standard Stars will have “a precision of 1 per cent or better” and that this is “twice the accuracy of current measurements” (6 February, p 13) what was he trying to tell us? Precision and accuracy are two very different things.

Take the distance from the centre of the Earth to the centre of the moon&colon; 240,000 miles would be an accurate but imprecise measurement; 289,562 miles would be precise but inaccurate; 238,857 miles would be both accurate and precise.